Amsonia — 'Blue Ice'
While some gardeners may plant bluestars for their blue flowers in early summer, this is one of those rare perennials with three seasons of interest. Once planted, this low maintenance plant needs little attention except to admire its beauty.
Bluestars (Amsonia), native to the south and central U.S, is named for an 18th century Virginia physician and scientific traveler in America, Dr. Charles Amson. So it is appropriate for native and naturalistic meadow plantings, as well as massed in borders or where you want a touch of blue. The blue flowers are small (about 1/2-inch wide) and, as the name indicates, star-shaped. They are borne in clusters (panicles) at stem ends, in some cases almost covering the plant for about one month in early summer in the north, late spring farther south.
This is one of those perennials some refer to as an “instant shrub.” Arising from the ground in spring, by summer it creates an upright, mounded shrub effect from 2 to 4 feet tall, depending on the species and growing conditions.
The long, narrow fruit pods (follicles) after bloom also are very attractive. It is one of the few perennials with very nice fall color—a soft golden yellow.
A member of the Dogbane family, related to the perennial periwinkle (Vinca) as well as the tropical frangipani (Plumeria), bluestars have a milky sap making them resistant to feeding by deer, other mammals, slugs and snails.
Bluestars require some cutting back in fall or early spring to a few inches above the ground. Full sun is needed for best growth and if too much fertility, or in too much shade, plants can become leggy. If this is the case, either stake or cut back about half-way after flowering. If in a long season and hot climate, you can cut back then to about 10 inches high.
Being tolerant of many conditions, bluestars are low maintenance. Keep any of the bluestars well-watered for the first season after planting. Once established they can tolerate some drought. Mulching will help conserve soil moisture. Fertilize lightly, if at all, to avoid leggy growth. A dressing of compost around plants in spring may be all this is required.
The Downy bluestar (A. ciliata) and the Ozark bluestar (A. hubrichtii) can be found naturally and grow well in drier sites. There are about 20 species, but only a handful are available at garden centers and nurseries.
The Ozark bluestar, sometimes called Arkansas or threadleaf bluestar, was chosen by professionals in the Perennial Plant Association as Perennial of the Year for 2011. Like most bluestars the leaves are longer than wide, but the leaves of this species are quite narrow. One common name indicates its origin, found in 1942 in the Ozark mountains of Arkansas by naturalist Leslie Hubricht. It grows best in USDA zones 6 to 8, sometimes into zone 5. While it can reach 3 feet high and wide in warmer climates, it may be less robust in cooler climates.
The most common bluestar is probably the Willow, the species named for German herbalist J.T. Tabernaemontanus.
While most bluestars only may grow into zone 5, this one is hardy in zones 3 through 9, and is found in moist woodlands. Its flowers are slate blue and the leaves wider than other species. Its fruit pods are held upright, unlike some other species whose pods hang down.
Eastern bluestar, a variety (salicifolia) of the Willow, has leaves five to 10 times as long as wide, like willow leaves (the species name is similar to the scientific name for willow).
Trials of several in this genus at the Chicago Botanic Garden (zone 5) several years ago resulted in good ratings for most.